Bone prosthesis for maintaining joint operation in complex joints

ABSTRACT

A prosthesis for reconstructing a multibone joint such as a wrist. A patient&#39;s scaphoid is removed to create a void. The scaphoid has a plurality of adjacent bones, each of the adjacent bones comprising a surface generally facing the void. The surface of at least two of the adjacent bones is prepared by affixing a magnetic element thereto and a magnetic scaphoid implant is inserted into the void. A magnetic relationship exists between the magnetic elements and the magnetic scaphoid implant.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of prior filed, pending U.S. patentapplication Ser. No. 13/731,160 filed Dec. 31, 2012, the disclosure ofwhich is incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates generally to joint repairs and replacements. Morespecifically, this invention relates to repairing a wrist by replacing abone proximate the joint with a prosthetic including a magnet.

BACKGROUND OF THE INVENTION

As is conventionally known, the wrist is a very intricateinterconnection of several bones, ligaments and tendons. The cooperationof these results in an elegant system allowing for varied and complexmovement. FIG. 1 shows the conventional structure, which includes fivemetacarpals 2, the radius 4, the ulna 6, and eight carpal bones. Thecarpal bones include the trapezium 10, the trapezoid 12, the capitate14, the hamate 16, the pisiform 18, the triquetrum 20, the lunate 22,and the scaphoid 24.

As illustrated in FIG. 1, outer surfaces of the scaphoid 24 cooperatewith corresponding surfaces of the surrounding carpal bones and theradius.

Arthritis of the wrist is a common ailment. There are multipleetiologies for the development of wrist degenerative arthritis,including trauma, inflammatory, and crystal induced. The two most commoncauses of wrist degenerative arthritis are scapholunate ligament tearsand scaphoid fractures. When a scapholunate ligament tear is leftuntreated, a progression of degenerative arthritis can occur, known asSLAC wrist. Scaphoid fractures that do not heal and that go ontonon-union develop a progression of wrist degenerative arthritis known asSNAC wrist.

In SLAC wrist, the progression of the degenerative arthritis originatesat the radial styloid. Due to the abnormal mechanics after ascapholunate ligament tear, the main stabilizer between the scaphoid andlunate is disrupted. As a result, the scaphoid flexes forward and thelunate and triquetrum extend dorsally. Due to the fact that the scaphoidis volar flexed it has difficulty clearing the radial styloid with wristflexion and extension, causing abnormal wear and degeneration at theradial styloid. This is the first stage of SLAC wrist degenerativearthritis.

The second stage occurs with increased abnormal mechanics at theradioscaphoid joint region. As a result of the scaphoid being in a moreflexed position, increased pressure and wear occur on the dorsal aspectof the scaphoid fossa articular surface of the distal radius and dorsalaspect of the scaphoid. With continued abnormal forces and wear,formation of degenerative arthritis occurs. In the third stage, thearthritis occurs at the capitolunate joint, and stage four occurs whenthe capitate head sinks deeper in the interval between the scaphoid andlunate. In many cases the radiolunate joint is spared, but not always.

In stage 1 of SNAC wrist, the distal pole of the scaphoid cannot clearthe radial styloid and degenerative arthritis occurs at the styloidregion. In stage 2, degenerative arthritis occurs at the radioscaphoidjoint. In stage 3 the arthritis occurs at the capitolunate joint.

In both types, the disease progression is fairly predictable.Conventional attempts at combatting arthritis at any stage generallyinclude reconstructive procedures such as removing carpal bones and/orfusing several of the carpal bones to each other as well as to theradius. These types of drastic procedure can severely limit motion ofthe wrist after surgery.

Accordingly, there is a need in the art for an improved method andprocedure for repairing the wrist.

As a result there is a need for a procedure that can recreate the normalanatomic relationship of the carpal bones, can recreate the normalanatomy and kinematics of the wrist in the earlier stages of thedisease, and will lead to improved functional outcomes as compared tothe reconstructive procedures that are used presently. To this end,there also is a need in the art for a procedure for replacing thescaphoid while maintaining relative movement of the carpal bonesrelative to each other as well as relative to the radius and ulna.

SUMMARY OF THE INVENTION

This disclosure satisfies the foregoing need in the art by providing animproved method and apparatus for doing selective replacement ofportions of the wrist, including replacing only the scaphoid.

In one aspect of the invention, a method of reconstructing a wristincludes removing a patient's scaphoid to create a void. The scaphoidhas a plurality of surfaces and a plurality of adjacent bones that arealigned with the scaphoid surfaces, each of the adjacent bonescomprising a joint surface generally facing the void. The joint surfacesof at least two of the adjacent bones are prepared by affixing amagnetic element to the bone, and a scaphoid implant is inserted intothe void. A magnetic relationship exists between the magnetic element(s)and the scaphoid implant. More specifically, the magnetic element(s)and/or the scaphoid implant include a magnet.

In another aspect of the invention, a prosthesis includes a magneticimplant approximating the size of a bone to be replaced; a firstmagnetic bone implant securable to a first bone adjacent the bone to bereplaced; and a second magnetic bone implant securable to a second boneadjacent the bone to be replaced, wherein each of the first and secondmagnetic bone implants have a magnetic relationship with the magneticimplant.

In another aspect of the invention, a prosthesis includes a scaphoidimplant approximating the size of a scaphoid to be replaced, a firstbone implant securable to a first bone adjacent the scaphoid to bereplaced, and a second bone implant securable to a second bone adjacentthe scaphoid to be replaced. The first and second bone implants eachhave a magnetic relationship with the scaphoid implant.

In another embodiment of the invention as more joint surfaces areeffected by the disease process more magnetic connections are necessary.

These and other aspects and features of the invention will beappreciated with reference to the following detailed description andaccompanying figures, in which preferred embodiments of the inventionare described and illustrated.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is perspective view showing the anatomy of the human wrist.

FIG. 2 is a perspective view of a preferred embodiment of a wrist-repairapparatus according to this disclosure, in which a prosthesis replacesthe scaphoid.

FIG. 3 is a perspective view of another preferred embodiment of awrist-repair apparatus according to this disclosure.

FIGS. 4A-4I illustrate a method of repairing a wrist using the apparatusillustrated in FIG. 3.

FIG. 5 is a perspective view of yet another preferred embodiment of awrist-repair apparatus according to this disclosure.

FIG. 6 is a perspective view of a preferred embodiment of concepts ofthe invention used to repair an ankle

DETAILED DESCRIPTION OF THE INVENTION

As noted above, the present invention relates to joint replacement. Onepresent embodiment of the invention will be described with reference toFIG. 2.

As used herein, a “magnetic element” generally refers to a componentthat includes a magnet or that responds to a magnetic field, i.e., bybeing attracted to or repelled by a magnet.

A “magnetic implant” is a type of magnetic element that is implantedinto the body.

In FIG. 2, the bones of the wrist are illustrated. Specifically, themetacarpal bones 2, the radius 4 and seven of the carpal bones 10, 12,14, 16, 18, 20, 22 are illustrated. Different from the natural anatomyof the hand, however, the scaphoid has been removed from the handillustrated in FIG. 2. In its place, a magnetic implant, here a scaphoidimplant 100 has been inserted such that the implant 100 is alignedproximate to the adjacent bones. The implant 100 is illustrated ashaving a generally oblong shape, substantially similar to the shape ofthe removed scaphoid. Accordingly, the implant 100 is arranged proximatesurfaces of the trapezium 10, the trapezoid 12, the capitate 14, thelunate 22 and the radius 4.

In the embodiment of FIG. 2, the implant 100 features a series ofscaphoid implant magnetic elements 110, 112, 114, 122, 104 disposed onan external surface of the scaphoid implant 100. In the illustratedembodiment, each of the magnetic elements is a magnet arranged to faceone of the bones proximate the implant 100.

The scaphoid implant magnetic elements 110, 112, 114, 122, 104 cooperatewith magnetic elements disposed on each of the adjacent bones.Specifically, the scaphoid implant magnetic element 110 is arranged tocooperate with trapezium magnetic element 10 m disposed on the trapezium10, the scaphoid implant magnetic element 112 is disposed to cooperatewith a trapezoid magnetic element 12 m, which is disposed on thetrapezoid 12, the scaphoid implant magnetic element 114 is disposed tocooperate with a capitate magnetic element 14 m disposed on the capitate14, the scaphoid implant magnetic element 122 is disposed to cooperatewith a lunate magnetic element 22 m disposed on the lunate 22, and thescaphoid implant magnetic element 104 is disposed to cooperate with theradius magnetic element 4 m disposed on the radius 4. Each of thescaphoid implant magnetic elements 110, 112, 114, 122, 104 isillustrated as protruding from a surface of the implant 100. This is notrequired. For example, the magnetic elements may be imbedded in asurface of the implant 100. In one example, the implant 100 may includea series of bores or similar cutouts in its surface, each disposed toaccept the respective magnetic element. The magnetic elements may beretained in such a bore or opening using any conventional method,including but not limited to adhesive, press fit, and by othermechanical fasteners.

The trapezium magnetic element 10 m, the trapezoid magnetic element 12m, the capitate magnetic element 14 m, the lunate magnetic element 22 m,and the radius magnetic element 4 m all are illustrated as protrudingfrom a surface of the respective bone to which they are attached. Inpractice, the magnetic elements could be attached to the bone using anyknown method including adhesive or mechanical fastener, cement or screw.In addition in another embodiment the magnets could be flush with thesurface of the respective bone. As will be appreciated by those ofordinary skill in the art, the surface of the respective bone to whicheach of the magnetic elements is placed may require some preparationprior to attachment of the magnetic element. For example, each of thebone surfaces to which the magnetic elements are attached may need to bestripped of any ligament. Moreover, degenerated cartilage and bonematerial may necessarily be removed from the bone.

As indicated above, the magnetic implants disposed on the carpal bonessurrounding the removed scaphoid and the magnets disposed on thescaphoid magnetic implant cooperate with each other. Accordingly, theyare provided in a one-to-one correspondence, i.e., each magnetic elementin each carpal bone has a mating or coupling magnetic surface in thescaphoid magnetic implant. In one embodiment, both magnetic elements ineach of the respective couplings include magnets, which cooperate byhaving an opposite polarity, thus attracting each other. In thisembodiment, an attraction is made between the trapezium magnetic element10 m and the scaphoid implant magnet 110, the trapezoid magnetic element12 m and the scaphoid implant magnet 112, the capitate magnetic element14 m and the scaphoid implant magnet 114, the lunate magnetic element 22m and the scaphoid implant magnet 122, and the radial magnetic element 4m and the scaphoid implant magnet 104. Each of the scaphoid implantmagnets may have a north polarity while the bone magnetic elementsdisposed on the carpal bones and the radius will have a south pole. Ofcourse, this arrangement could be reversed. Moreover, some of theimplant magnets could have a north polarity while others have a southpolarity. The respective coupling carpal bone or radius magneticelements have the opposite polarity in this arrangement.

In still other embodiments of the invention, it may be desirable thatthe respective implant and bone magnet couples repel each other. In onesuch embodiment, the scaphoid implant 100 would be repelled by themagnetic elements associated with each of the carpal bones 10, 12, 14,22 and the radius 4, causing the scaphoid implant to remain suspendedbetween each of the bones. In other arrangements, some scaphoidimplant/bone magnet couples could attract while others could repel.

According to the embodiments just described, the functionality of thewrist after inserting the implant 100 is substantially the same as priorto surgery and removal of the scaphoid. The magnet pairs preferably,whether attracted or repelled relative to each other, will move relativeto each other in a sliding engagement, as necessary, recreating thenormal kinematics of the wrist. Thus, the drawbacks of a complete wristfusion are avoided, but the defective scaphoid and degenerative surfacesof the adjacent bones are removed, thereby providing pain relief andincreased function.

Although FIG. 2 shows five magnet pairs, other embodiments also arecontemplated. For example as few as two magnet pairs could be included.In preferred embodiments, those pairs could include the implant magnet112 and the trapezoid magnet 12 m and the implant magnet 104 and radiusmagnet 4 m. Similarly, the pairs may be the implant magnet 110 and thetrapezium magnet 10 m and implant magnet 122 and lunate magnet 22 m. Ineach of these alternative embodiments, the magnet pairs may preferablybe disposed proximate opposite sides of the scaphoid implant 100,although such is not necessary. The magnet pairs may instead be disposedon adjacent bones such as on the lunate and the capitate, by way ofnon-limiting example.

In accordance with another alternative embodiment of the invention, theimplant magnets 110, 112, 114, 122, 104 or the magnetic elementsattached to the bones 10 m, 12 m, 14 m, 22 m, 4 m may not be magnets atall. Instead, one or the other could be a ferrous material or analternative material that responds to a magnetic field so as to beattracted (or repelled) by the magnet disposed on the adjacent surface.For example, each of the implant magnets 110, 112, 114, 122, 104 couldbe a ferrous material instead of a magnet, and thus would be attractedto each of the magnets disposed on the carpal bones and the radius. In asimilar embodiment, the implant 100 may simply be made of a ferrousmaterial, which would be attracted to the magnets disposed on the bones.This arrangement would alleviate the need for separate componentsattached to the implant 100, such as those surfaces illustrated byreference numerals 110, 112, 114, 122, and 104. Although adjacentsurfaces of the bone and the magnetic material are shown as beinggenerally planar, this is not required. For example, the magnets mayhave surface curvature which may approximate the curvature of thescaphoid and/or other, adjacent bones.

In yet another embodiment of the invention, the scaphoid implant 100 maybe a magnet, and the bone magnetic elements represented by referencenumerals 10 m, 12 m, 14 m, 22 m, and 4 m may be ferrous surfaces ormagnets of opposite polarity. The ferrous surfaces may be implanted, ormay simply be added to a screw or the like that is fastened to the bone.In this embodiment, the implant 100 will attract each of the implantsplaced in the proximate bones, resulting in a similar arrangement asdescribed above.

Depending upon the strength of the magnets used, the embodiments of theinvention may further require a shield that is placed over the magneticcomponents of the invention, i.e., to limit the impact of the magneticfield beyond the inside of the wrist. For example, it may be desirableto shield the magnetic components to prevent accidental attraction orrepulsion of the magnetic components to metal or magnets in theenvironment that the user may operate or handle with the hand having thereplaced wrist.

A preferred method of using an implant 100 such as described abovegenerally includes making an incision in the user's wrist. This iscommon with a conventional wrist replacement surgery. The scaphoidpreferably is freed from adjacent bones and tissue by cutting connectivetissue, and is then removed from the wrist entirely. The surfaces of thetrapezium 10, trapezoid 12, capitate 14, lunate 22 and the radius 4 thatarticulate with the scaphoid are then prepared by removing anyconnective tissue and degenerated cartilage and bone, as appropriate.

An implant or a component is then fixed to each of those preparedsurfaces. For example, the implant may be the bone magnetic elements 10m, 12 m, 14 m, 22 m, and 4 m described above. As noted above, themagnets may be fixed to the surface of the bones by any conventionalmeans including adhesive and mechanical fasteners, such as bone cement.In one embodiment, the magnet is arranged on the head of a screw, suchas a surgical screw, which would be inserted into the bone in aconventional manner by a surgeon. Once each of the surfaces has beenprepared, the scaphoid implant 100 is put into place between thosesurfaces. The scaphoid implant 100 may be sized such that it is pressedinto the opening between the prepared surfaces with force. Once pressedinto place, the magnetic relationship between the scaphoid implantmagnetic elements 110, 112, 114, 122 and 104 and the bone magneticelements 10 m, 12 m, 14 m, 22 m, and 4 m act to retain the scaphoidimplant 100 in place. As required, a shielding mechanism may be placedover the magnets. The shield is so placed to shield the magnetic fieldfrom affecting any area outside of the wrist. In one embodiment, themagnets and the shielding mechanism may be integrally formed. Forexample, the magnets may be generally cylindrical in shape, with acenter, cylindrical region that is magnetized and a surroundingcylindrical region that is non-magnetized. This non-magnetized regioncould actually act to dissipate the magnetic field of the centralmagnet, so the magnetic field acts substantially only at the ends of themagnet. The procedure is completed by suturing the incision closed.

Another embodiment of the invention is illustrated in FIG. 3, in which asingle magnetic element is included as a plate 211, spanning andattached to both the trapezium 10 and the trapezoid 12. As illustratedby this embodiment, it is not required that the magnetic bone implantsand the bones have one-to-one correspondence as in the priorembodiments, but instead a single magnetic implant may be fixed to morethan one bone. In this embodiment, the scaphoid implant 200 is magneticand the magnetic bone implant 211 spanning the trapezium 10 and thetrapezoid 12 has an opposite polarity, such that the magnetic boneimplant 211 is attracted to the scaphoid implant 200.

Also in this embodiment, an insert 213 is fastened to the magnetic boneimplant 211 such that the insert 213 is arranged on a face of the boneimplant 211 facing the scaphoid implant 200. The insert 213 is disposedfor contact by the scaphoid implant 200, and provides a surface uponwhich the implant 200 moves freely. In a preferred embodiment, theinsert 213 is made of a biocompatible material having a low coefficientof friction. Examples of such materials include polymers such aspolyethylene, ceramics, and pyrolytic carbon (pyrocarbon). The insert213 is preferably to provide a smooth gliding surface to preventmetal-on-metal wear, especially because the opposing implant contactsurfaces will move relative to each other. Also the insert will be thinenough and be made of appropriate material to allow unimpeded attractionof magnetic surfaces on opposing sides of the insert 213.

The implant 213 preferably is fixed to the magnetic bone implant 211.Fasteners may be used to this end, but in a preferred embodiment theinsert is sized to be snapped onto the magnetic bone implant 211. In oneembodiment, edges of the insert have one or more extensions that engageover the sides of the bone implant 211. In another embodiment, the boneimplant has one or more bores drilled therein and the insert has matingprotrusions on the surface facing the bone implant 211. The protrusionsare press fit into the bores to retain the insert 213 on the implant211. Those of ordinary skill in the art will appreciate additionalmechanisms for retaining the insert 213 on the implant 211.

The insert 213 preferably is contoured to accommodate the contour of thescaphoid implant 200, i.e., such that the scaphoid implant 200 and theinsert 213 articulate relative to each, as in normal wrist operation.Moreover, and as will be described in more detail below, the boneimplant 211 and insert 213 preferably are positioned to closelyapproximate the pre-surgery size and shape of the trapezium andtrapezoid original surfaces.

Also illustrated in FIG. 3 is a second magnetic implant 204, provided onthe distal radius 4, and having the same polarity as the first magneticbone implant 211 spanning the trapezium 10 and the trapezoid 12. Thesecond magnetic bone implant 204 preferably is inserted into the distalradius and an insert 205 is disposed thereon, much like the insert 213described above. Also shown in FIG. 3 are magnetic implants, which areillustrated as substantially cylindrical magnets 214 and 222 disposed onthe capitate 14 and the lunate 22, respectively. Fixation methods suchas those described above may be used to affix the magnets to therespective bones. For example, the first magnetic implant 211 is screwedinto the trapezium 10 and the trapezoid 12 in the illustration usingsurgical screws 230. The second magnetic bone implant 204 may be pressfit into a cup or indentation formed in the distal radius 4, or it couldbe affixed using screws, adhesives or any other known method.

A preferred method of implementing the prosthetic system of FIG. 3 nowwill be described with reference to FIGS. 4A-4I.

As illustrated in FIG. 4A, the defective scaphoid is first removed. Aswill be appreciated by those having ordinary skill in the art, thescaphoid is accessed by making necessary incisions, opening the wristcapsule, and removing ligaments, as required. As also illustrated inFIG. 4A, the surfaces 10 a, 12 a of the trapezium 10 and the trapezoid12 that articulate relative to the scaphoid are precisely prepared byremoving any and all arthritic bone and cartilage, using conventionaltools, such as surgical saws, chisels, and the like. Jigs also may beconstructed particularly for use in the method. A small amount ofsubchondral bone also is removed, but much of the trapezium 10 and thetrapezoid 12 are left in place.

As illustrated in FIG. 4B, the first magnetic bone implant 211 is fixedto the prepared trapezium 10 and the trapezoid 12. In the illustration,surgical screws 230 are used to retain the plate 211. The screws 230 areillustrated as extending into the trapezium 10 and the trapezoid 12. Inother embodiments, the screws may extend into the metacarpals, which mayincrease stability. Alternatively, or in addition, cement or glue may beused to fix the first magnetic bone implant 211. The surface of theimplant 211 contacting the trapezium and the trapezoid preferably hasbone ingrowth surfaces, as are conventional in the art.

In FIG. 4C, the insert 213 is fixed to the first magnetic bone implant.As detailed above, the insert is preferably a thin, low-frictionmaterial upon which a scaphoid implant 200 will freely articulate. Theinsert 213 may be contoured to accommodate the scaphoid implant 200.

In FIG. 4D, the surgeon removes any arthritis from the portion of theradius surface that articulates with the scaphoid, namely, the radialscaphoid fossa, as well as a small amount of subchondral bone. Afterprepared, the radial fossa preferably has a concave shape. A bore hole(not shown) also may be drilled longitudinally into the radial fossa.The bore may be provided, to receive a spike, keel or similar protrusionon the second magnetic bone implant 204. In other embodiments, the spikeor keel may be driven directly into the bone.

In FIG. 4E, the second bone implant 204 is fixed to the prepared surfaceof the radial fossa. The implant 204 may be fixed with screws, adhesive,cement, or press fit or any known methodology. In the illustratedembodiment, a keel protrudes from the back surface of the secondmagnetic bone implant 204 and the implant 204 is hammered into theradius. The keel provides increased fixation and stability to theimplant. In other embodiments, other fasteners, such as screws, may beused for secure affixation.

In FIG. 4F, the insert 205 is fixed to the second magnetic bone implant204. As with the insert 213, the insert 205 preferably snaps onto theimplant 204, although other attachment means may be used. Also as withthe insert 213, the radial implant insert is made of a material such aspolyethelene or ceramic to provide a smooth gliding surface between theimplants.

Next, as shown in FIG. 4G, the surgeon drills bore holes into thecapitate 14 and the lunate 22, and in FIG. 4H the magnets 214, 222 arepressed into the bores. The magnets 214, 222 preferably are press fitinto the bore holes, although they may be retained in the capitate 14and lunate 22 by any conventional means. As with the first magnetic boneimplant 211 and the second magnetic bone implant 204, the magnets 214,222 preferably include porous ingrowth surfaces. An insert (not shown)also may be provided on each of the magnets 214, 222, to minimizefriction between the magnets 214, 222 and the implant 200 (shown in FIG.4I). Such an insert could be similar to the inserts 205, 213.

In FIG. 4I, the scaphoid implant 200 is placed in the void bounded bythe inserts 205, 213. In the preferred embodiments, the surfaces of theinserts 205, 213 and of the magnets 214, 222 form a void for receivingthe scaphoid implant 200. Each of those surfaces is disposedapproximately at the position of the removed surface of the originalbone and preferably has a concave surface. Moreover, as illustrated, themajority of the original surfaces of the lunate and capitate that facethe scaphoid and in which the magnets 214, 222 are placed, aremaintained, because the disease process generally will not affect thosesurfaces. For instance, the surface of the insert 205 approximates theposition, contour and size of the original radius surface. Accordingly,the scaphoid implant 200 approximates the size and shape of the removedscaphoid (pre-injury). In this manner, the reconstructed anatomy of thewrist is substantially the same as the original anatomy of the wrist. Inone preferred embodiment, the scaphoid implant is placed into the voidto cooperate with recessed or concave areas of the magnets/implantsplaced in the trapezium, trapezoid, and radius, for example. To thisend, those surfaces may have a generally concave shape to receive agenerally convex feature on the outer surface of the scaphoid implant.This relationship between the concave and convex surfaces, combined withthe attractive forces between the magnetic implant 200 and the magneticimplants 211, 204 and magnets 214, 222, hold the implant in place. Thesurgery is completed by closing up any incisions. As will beappreciated, the size and features of the implants, magnets and plates,including the convex and concave shapes of the implant and the platesfixed to the bones, are intended to closely recreate the originalphysiology and functioning of the wrist.

In the embodiment described in connection with FIGS. 3 and 4A-4I, thebone implants 211, 204 are magnets. That is, they may be a magnetizedplate. Alternatively, the implants may be made of more than onecomponent, for example, a non-ferrous plate or component with one ormore attached magnets. The non-ferrous material may be non-metallic,such as, pyrocarbon or ceramic, which could alleviate the need for aninsert, i.e., because there would be minimal friction between theimplant and the scaphoid implant 200. In other embodiments, the insertmay still be used. Moreover, although in the embodiments described abovethe insert is applied to the magnetic implants after those implants areaffixed to the bone, the inserts could be applied to the magnets beforethe magnets are attached to the respective bones.

The magnets described in this disclosure preferably have up to 5000Gauss surface strength. They are made from any number of materials,including neodymium, metal alloy, ceramic or rubberized magneticmaterial. The inserts are preferably relatively thin members, such thatthey do not impede the magnetic attraction between the implant 200 andthe surrounding magnets/implants.

FIGS. 3 and 4A-4I generally illustrate a methodology for replacing ascaphoid in a manner that closely approximates pre-injury wristkinematics and physiology. According to the methods described above,injured bone and/or tissue are replaced, but the remainder of the wristis left intact. In a preferred embodiment, as much as possible of theoriginal wrist structure is left in place. This methodology is in starkcontrast to previous methods in which an entire row or more of carpalbones are removed and remaining structure is fused.

However, the invention is not limited to replacing only the scaphoid. Asdescribed in the Background of the Invention section, common wristarthritis diseases follow a common pattern. The embodiments describedabove are generally successful at repairing a SLAC or SNAC wrist that isat Stage 1 and even Stage 2. Further progressed arthritis, though, maynot be fixed by replacing only the scaphoid. If the injury is notdiagnosed until farther along in the process, the composition of thecapitate may also be compromised. In such a situation, anotherembodiment of the invention contemplates providing a capitate implant,such as is illustrated in FIG. 5. It is at the discretion of the surgeonwhether such an additional implant is indicated based on the severity ofthe disease process.

In FIG. 5, the scaphoid and capitate have been replaced, respectively,with a scaphoid implant 200 and a capitate implant 300. Like in previousembodiments, the bones surrounding those implants are prepared, e.g., byremoving diseased surfaces, and bone magnetic elements are attachedthereto. The scaphoid and capitate implants 200, 300 are then insertedinto the respective voids created by removing the native bones. In apreferred embodiment, the scaphoid and capitate implants 200, 300 areattracted to each other, as is generally illustrated in FIG. 5.

In the illustration, two lunate magnetic elements 222 a, 222 b areplaced in the lunate, the first element 222 a for communicating with thescaphoid implant 200 in the same manner as the lunate magnetic element222 described above and the second element 222 b for communicatingmagnetically with the capitate implant 300. Also in FIG. 5, a hamatemagnetic member 216 is affixed to the hamate 16 in a position to have amagnetic relationship with the capitate implant 300. A metacarpalmagnetic implant 202 also is provided on the third metacarpal, forcooperating magnetically with the capitate implant 300 and an insert 203is provided on the metacarpal magnetic implant 202. As illustrated, themagnetic elements 222 a, 222 b, and 216 are similar to magnetic elementsdescribed above, which are inserted into bore holes formed in therespective bone, and the metacarpal magnetic implant 202, is similar incomposition to the implants 204, 211. This alternative embodiment is notlimited to these arrangements. Generally speaking, the specifics of thetype, size, and placement of the magnetic implants will be dictated bythe procedures undertaken to remove diseased areas from surroundingbones.

Like in previous embodiments, in the embodiment of FIG. 5 other bonesand structure in the joint are not affected by the prosthesis. So, forexample, native structure is left intact where possible, while diseasedsurfaces and bones are repaired. The magnetic relationships between themagnetic implants, the scaphoid implant, and the capitate implant act toprovide proper orientation of the components, essentially serving as“magnetic ligaments.” The overall result is a reconstructed wrist withoperation that very closely approximates pre-injury operation.

As should be appreciated by those having ordinary skill in the art,other or additional bones in the wrist could also be replaced with asimilar implant, for example, because the disease has furtherprogressed.

Although the invention has been described in terms of replacing a wrist,it may be used in other instances. Specifically, the novel conceptsdescribed herein may be used in other instance of complex joints thatinclude more than three bones that move relatively.

For example, FIG. 6 illustrates a foot 402 in which the talus has beenreplaced with a talus implant 500. Like in the embodiments describedabove, surfaces of the navicular, the tibia and fibula, and/or thecalcaneus may be freed from arthritis or other disease and fitted with amagnetic implant that cooperates with the talus implant to recreateanatomy prior to the injury. In FIG. 6, a calcaneus magnetic implant 630is provided in the calcaneus 30 and a navicular magnetic element 632 isprovided in the navicular 32. As will be appreciated, other oradditional bones also may include magnetic elements, and the inventionis not limited to the magnetic elements illustrated. For example FIG. 6also illustrates a fibular magnetic element 634 and a tibial magneticelement 636. Those elements are disposed at the distal end of the fibulaand tibia, and are similar in construction and application to the radialmagnetic element 204 shown in FIG. 3, disposed in the radius. Althoughnot illustrated, an insert may be disposed on each of the fibular andtibial magnetic elements 634, 636. In other embodiments, other bones maybe replaced with an implant. Moreover, the invention is not limited tothe illustrated magnetic attachments; any of the magnetic attachmentsdescribed in the disclosure can be used to hold the talus implant 500 inplace. As should be appreciated, the invention is particularly useful incomplex joints like the wrist, ankle and foot, where the joint comprisesa plurality of bones, and those bones move relative to each other.

The invention also is not limited to application in humans. Those havingordinary skill in the art will appreciate many additional applications,such as in animal applications.

While the invention has been described in connection with severalpresently preferred embodiments thereof, those skilled in the art willappreciate that many modifications and changes may be made withoutdeparting from the true spirit and scope of the invention whichaccordingly is intended to be defined solely by the appended claims.

1. A prosthesis comprising: a magnetic implant approximating the size ofa bone to be replaced; a first magnetic bone implant securable to afirst bone adjacent the bone to be replaced; and a second magnetic boneimplant securable to a second bone adjacent the bone to be replaced,wherein each of the first and second magnetic bone implants have amagnetic relationship with the magnetic implant.
 2. The prosthesis ofclaim 1, wherein the magnetic implant is a scaphoid implantapproximating the size of a scaphoid to be removed from a patient'swrist, the first magnetic bone implant is securable to a first boneadjacent the scaphoid to be replaced, and the second magnetic boneimplant is securable to a second bone adjacent the scaphoid to bereplaced, wherein the first and second magnetic bone implants each havea magnetic relationship with the scaphoid implant.
 3. The prosthesis ofclaim 2, wherein the scaphoid implant comprises a magnet.
 4. Theprosthesis of claim 2, wherein at least one of the first magnetic boneimplant and the second magnetic bone implant comprise a magnet.
 5. Theprosthesis of claim 2, wherein the first magnetic bone implant comprisesa first magnet, the second magnetic bone implant comprises a secondmagnet and further comprising one or more additional magnets, the one ormore additional magnets being securable to additional bones adjacent thescaphoid to be replaced.
 6. The prosthesis of claim 5, wherein thefirst, second, and one or more additional magnets are securable to thetrapezium, the trapezoid, the lunate, the capitate or the radius.
 7. Theprosthesis of claim 2, wherein at least one of the first magnetic boneimplant and the second magnetic bone implant comprises a magneticelement and an insert disposed on the magnetic element, the magneticimplant contacting the insert.
 8. The prosthesis of claim 7, wherein theinsert is a biocompatible material with a low coefficient of friction.9. The prosthesis of claim 7, wherein the insert is made of one ofpolyethylene, ceramic, and pyrolytic carbon.
 10. The prosthesis of claim2, further comprising a shield disposed on at least one of the magneticimplant, the first magnetic bone implant, and the second magnetic boneimplant.
 11. The prosthesis of claim 1, wherein the magnetic implantcomprises a magnet.
 12. The prosthesis of claim 1, wherein at least oneof the first magnetic bone implant and the second magnetic bone implantcomprise a magnet.
 13. The prosthesis of claim 12, wherein the firstmagnetic bone implant comprises a first magnet, the second magnetic boneimplant comprises a second magnet and further comprising one or moreadditional magnets, the one or more additional magnets being securableto additional bones adjacent the bone to be replaced.
 14. The prosthesisof claim 1, wherein at least one of the first magnetic bone implant andthe second magnetic bone implant comprises a magnetic element and aninsert disposed on the magnetic element, the magnetic implant contactingthe insert.
 15. The prosthesis of claim 14, wherein the insert is abiocompatible material with a low coefficient of friction.
 16. Theprosthesis of claim 14, wherein the insert is made of one ofpolyethylene, ceramic, and pyrolytic carbon.
 17. The prosthesis of claim1, further comprising a shield disposed on at least one of the magneticimplant, the first magnetic bone implant, and the second magnetic boneimplant.
 18. The prosthesis of claim 1, wherein the magnetic implantcomprises a magnet and at least one of the first magnetic bone implantand the second magnetic bone implant is attracted to the magnet.
 19. Theprosthesis of claim 1, wherein at least one of the first magnetic boneimplant and the second magnetic bone implant comprises a magnet and themagnetic implant is attracted to the magnet.
 20. The prosthesis of claim1, wherein each of the magnetic implant and the first and secondmagnetic bone implants comprise magnets.